Various classes of dressings are currently used in the management of acute and chronic dermal wounds. Of these, the hydrocolloid dressings (HCD) dressings are used most frequently in the clinical setting. The high absorptive capacity characteristic of these dressings coupled with the occlusive and moist environment they provide lead to rapid granulation, re-epithelialization and wound closure.
Clinical applications for HCD dressings include the treatment of burns and burn donor sites, chronic venous ulcers, decubitus ulcers, leprous ulcers, epidermolysis bullosa, scleroderma, psoriasis and non-infected partial thickness wounds.
Conventional HCD dressings incorporate an adhesive mixture, usually composed of low and high molecular weight polyisobutylene, and absorbents such as gelatin, pectin and carboxymethyl cellulose, silica and cotton fibers. Representative HCD dressings are described, for example, in U.S. Pat. Nos. 3,972,328 (Aug. 3, 1976) to Chen, et al, 4,253,460 (Mar. 3, 1981) to Chen, et al, and 4,538,603 (Sep. 3, 1985) to Pawelchak, et al.
Residual material components from HCD dressings have often been noted in the healing wound. In most cases, despite the presence of such extraneous substances, wounds re-epithelialize and close in the course of time, with no externally visible abnormalities. Recently reported histologic evaluations, however, of such apparently healed wounds in animals have indicated deep-seated foreign body type reactions and granulomata formations (Young, et al, Journal of Investigative Dermatology, vol. 97, pgs. 586-592, 1991). These effects have been attributed to the dressing residues that remain in the wound after healing and closure. The clinical relevance and the long-term implications of such deep-seated chronic inflammation is still unknown. However, the presence of inflammatory dressing residues can be expected to extend the inflammatory phase of wound healing and thus adversely affect the processes of granulation, matrix formation, tissue remodeling, re-epithelialization, and wound closure. Despite these recently raised questions, it is likely that HCD dressings will remain in widespread clinical use for the treatment of dermal wounds. Elimination of both acute and chronic foreign body-type reaction from HCD dressings is therefore a desirable goal.
Various absorbents are currently used in the formulation of wound fillers and dressings. The key feature of these absorbents in their choice as wound dressing components appears to be their fluid handling capacity; biodegradability has not been an issue of major concern. In view of this, it is not surprising that recent histological studies show that the use of certain wound dressings lead to extensive non-resolved and deepseated chronic inflammation in externally healed tissue. Such inflammation can potentially be reduced by using dressing components that degrade to non-toxic and non-inflammatory products under physiological conditions. In this context it should be noted that none of the commonly used biodegradable microspheres in controlled drug delivery (such as polylactides or gylcollides) possess any appreciable absorptive or fluid handling capacity.
Young, et al, cited supra describes a study which compares the effects of a semi-occlusive adhesive polyurethane dressing with a hydrocolloid dressing. The deep seated chronic inflammation noted with the hydrocolloid dressing was not observed with the semi-occlusive dressing. On the other hand, semi-occlusive dressings do not have the capacity to absorb wound exudate which is a key characteristic of hydrocolloid dressings.
Improvements in hydrocolloid dressing formulation is a desirable approach in order to eliminate both acute and chronic foreign body-type reactions of presently known hydrocolloid dressings while preserving the capacity to absorb exudate which is also characteristic of hydrocolloid dressings. In particular, a hydrocolloid dressing component which is both absorptive and biodegradable is needed.